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CHEMINFO Record Number: 473
CCOHS Chemical Name: Isophthalic acid

Benzene-1,3-dicarboxylic acid
1,3-Benzenedicarboxylic acid
m-Benzenedicarboxylic acid
1,3-Phthalic acid
m-Phthalic acid
Phthalic acid (non-specific name)

Chemical Name French: Acide isophtalique
Chemical Name Spanish: Acido isoftalico

Trade Name(s):

CAS Registry Number: 121-91-5
RTECS Number(s): NT2007000
EU EINECS/ELINCS Number: 204-506-4
Chemical Family: Aromatic carboxylic acid / aromatic dicarboxylic acid / benzenecarboxylic acid / benzenedicarboxylic acid / phthalic acid isomer
Molecular Formula: C8-H6-O4
Structural Formula: HO-C(=O)-C6H4-C(=O)-OH


Appearance and Odour:
White crystals or powder.(5,6) Slight, unpleasant odour.

Odour Threshold:
No information was located

Warning Properties:
Insufficient information for evaluation.

Isophthalic acid is one of three chemical forms (isomers) of benzenedicarboxylic acid (1,3-benzenecarboxylic acid). 1,2-Benzenecarboxylic acid is commonly known as phthalic acid and 1,4-benzenecarboxylic acid as terephthalic acid. For information on these related acids refer to CHEMINFO records 472 and 474 respectively. Isophthalic acid is commercially available in a purified grade (greater than 99.9 weight % pure, exclusive of some residual water). It may contain trace impurities such as 3-formylbenzoic acid, m-toluic acid, benzoic acid and trace metals, residual water and ash (trace metal oxides).(2)

Uses and Occurrences:
Used in the manufacture of unsaturated polyester resins or isopolyesters; in alkyd coatings; as a minor co-monomer with terephthalic acid in saturated polyesters; in production of polyester beverage bottles; in formulations for adhesives, inks, wire enamels and dental materials; in plasticizers; and as a chemical intermediate for isophthalate diesters.(2,5)


White crystals or powder, with a slight unpleasant odour. Can burn if strongly heated. COMBUSTIBLE DUST. Can form explosive dust-air mixtures. Essentially non-toxic following short-term contact.


Effects of Short-Term (Acute) Exposure

In general, high concentrations of dust may cause coughing and mild, temporary irritation. Animal information indicates that short-term inhalation toxicity is low. There is no human information available.

Skin Contact:
Isophthalic acid is probably not irritating to the skin, based on unconfirmed animal information and comparison to terephthalic acid. There is no specific human or animal information available.
Isophthalic acid is probably not absorbed through the skin, based on unconfirmed animal information and comparison to terephthalic acid.

Eye Contact:
The dust can probably cause mild irritation, based on one unconfirmed animal study. In general, dusts are irritating as "foreign objects". Some tearing, blinking and mild temporary pain may occur as the solid material is rinsed from the eye by tears. There is no human information available.

Unconfirmed animal information indicates that oral toxicity is extremely low. There is no human information available. Ingestion is not a typical route of occupational exposure.

Effects of Long-Term (Chronic) Exposure

There is no human information available.

INGESTION: Ingestion of very high dietary levels may cause bladder and kidney stones, based on the results of one animal study and comparison to related chemicals. These levels are not relevant to occupational exposures.


There is no human information available. Kidney cancer observed in rats is believed to be secondary to the formation of kidney stones and not direct carcinogenicity.(1)

The International Agency for Research on Cancer (IARC) has not evaluated the carcinogenicity of this chemical.

The American Conference of Governmental Industrial Hygienists (ACGIH) has no listing for this chemical.

The US National Toxicology Program (NTP) has not listed this chemical in its report on carcinogens.

Teratogenicity and Embryotoxicity:
There is no human information available. One unconfirmed animal study showed no teratogenic effects.

Reproductive Toxicity:
There is no human or animal information available.

There is no human or live animal information available. Negative results have been obtained in tests using cultured mammalian cells. Positive and negative results have been obtained in tests using bacteria.

Toxicologically Synergistic Materials:
There is no information available.

Potential for Accumulation:
Isophthalic acid probably does not accumulate in the body, based on information for terephthalic acid, a closely related acid. It is probably rapidly excreted unchanged, mainly in the urine, with small amounts in the feces.


No health effects expected. If symptoms develop, remove source of contamination or have victim move to fresh air. If symptoms persists, obtain medical advice immediately.

Skin Contact:
If irritation occurs, gently blot or brush away excess chemical quickly. Wash gently and thoroughly with water and non-abrasive soap. If irritation persists, obtain medical advice immediately. Completely decontaminate clothing, shoes and leather goods before re-use or discard.

Eye Contact:
Do not allow victim to rub eye(s). Let the eye(s) water naturally for a few minutes. Have the victim look right and left, and then up and down. If particle/dust does not dislodge, flush with lukewarm, gently flowing water for 5 minutes or until particle/dust is removed, while holding the eyelid(s) open. If irritation persists, obtain medical attention. DO NOT attempt to manually remove anything stuck to the eye(s).

If irritation or discomfort occur, obtain medical advice immediately.

First Aid Comments:
All first aid procedures should be periodically reviewed by a doctor familiar with the material and its conditions of use in the workplace.


Flash Point:
Not applicable.

Lower Flammable (Explosive) Limit (LFL/LEL):
Not applicable

Upper Flammable (Explosive) Limit (UFL/UEL):
Not applicable

Autoignition (Ignition) Temperature:
647.8 deg C (1198 deg F) (6)

Sensitivity to Mechanical Impact:
Not sensitive. Stable material.

Combustion and Thermal Decomposition Products:
Carbon monoxide and carbon dioxide and other toxic chemicals.(6) Incomplete combustion may also produce acrid smoke and irritating fumes.

Flammable Properties:

Specific Hazards Arising from the Chemical:
During a fire, irritating/toxic gases and fumes may be generated.

Extinguishing Media:
Dry chemical powder, carbon dioxide, alcohol foam, polymer foam, water spray or fog.(2,6)

Fire Fighting Instructions:
Evacuate area and fight fire from a safe distance or a protected location. Approach fire from upwind to avoid toxic decomposition products.
Water or foam may cause frothing. The frothing may be violent and could endanger personnel close to the fire. However, a water spray or fog that is carefully applied to the surface of the burning material, preferably with a fine spray or fog nozzle, will cause frothing that will blanket and extinguish the fire. In addition, water spray or fog can be used to prevent dust formation, absorb heat, keep containers cool and protect exposed material. Water spray may be used to flush spills away from ignition sources. Solid streams of water may be ineffective and spread material.
The decomposition products of isophthalic acid may be hazardous to health. Firefighters may enter the area if positive-pressure self-contained breathing apparatus (MSHA/NIOSH approved or equivalent) and full Bunker Gear is worn.


NFPA - Comments:
NFPA has no listing for this chemical in Codes 49 or 325.


Molecular Weight: 166.14

Conversion Factor:
Not applicable

Physical State: Solid
Melting Point: 345-348 deg C (653-658.4 deg F) (closed tube); 384 deg C (723.2 deg F) (2)
Boiling Point: Sublimes without decomposition.(5,10)
Relative Density (Specific Gravity): 1.507 at 20 deg C (water = 1) (5)
Solubility in Water: Practically insoluble (12 mg/100 g) (2,10,11)
Solubility in Other Liquids: Soluble in ethanol, dimethylformamide and dimethyl sulfoxide; moderately soluble in methanol and 1-propanol; slightly soluble in glacial acetic acid; insoluble in benzene, toluene, ligroin, petroleum ether, and diethyl ether.(2,5,10,11)
Coefficient of Oil/Water Distribution (Partition Coefficient): Log P(oct) = 1.66 (5,12)
pH Value: 3.36 (saturated solution (0.012% in water)) (calculated)
Vapour Density: Not applicable
Vapour Pressure: Very low at room temperature; 0.009 kPa (0.068 mm Hg) at 100 deg C (2,5)
Saturation Vapour Concentration: Very low at normal temperatures.
Evaporation Rate: Probably very low at normal temperatures.
Critical Temperature: 734 deg C (1353 deg F) (5)

Other Physical Properties:
ACIDITY: Weak acid; pKa1 = 3.62 (Ka1 = 2.4 X 10(-4)); pKa2 = 4.60 (Ka2 = 2.5 X 10(-5)) (2,11); pKa1 = 3.70; pKa2 = 4.60 at 25 deg C.(5)
CRITICAL PRESSURE: 395O kPa (39 atm) (5)


Normally stable

Hazardous Polymerization:
Does not occur

Incompatibility - Materials to Avoid:

NOTE: Chemical reactions that could result in a hazardous situation (e.g. generation of flammable or toxic chemicals, fire or detonation) are listed here. Many of these reactions can be done safely if specific control measures (e.g. cooling of the reaction) are in place. Although not intended to be complete, an overview of important reactions involving common chemicals is provided to assist in the development of safe work practices.

STRONG OXIDIZING AGENTS (e.g. perchlorates, peroxides, chlorine) - react violently or explosively. Increased risk of fire and explosion.(6)
CONCENTRATED NITRIC ACID - may form explosive mixtures.
ACTIVE METALS (e.g. aluminum or zinc) - may evolve flammable and potentially explosive hydrogen gas.(13)
STRONG BASES (including alkalis such as sodium hydroxide) - react vigorously.(6)

Hazardous Decomposition Products:
None reported

Conditions to Avoid:
Generation of dust, heat, flames, sparks, build-up of static electricity and other ignition sources.

Corrosivity to Metals:
Specific information is not available. May be corrosive to some metals in the presence of moisture or water. Saturated solutions of phthalic acid, a closely related acid, produce corrosive effects on cast iron and steel.(14) Acids are generally not corrosive to types 304 and 316 stainless steels, and aluminum is generally resistant to acids at room temperature.(15)

Stability and Reactivity Comments:
Probably may attack some forms of plastics, rubber and coatings.(13)


LD50 (oral, rat): 10400 mg/kg (2,3, unconfirmed)

LD50 (dermal, rabbit): greater than 2000 mg/kg (4, unconfirmed)

Eye Irritation:

Mild irritation was observed in rabbits following application of 500 mg in a standard Draize test.(3, unconfirmed)

Skin Irritation:

No irritation was observed (dermal irritation score 0/8) in rabbits.(4, unconfirmed)

Effects of Short-Term (Acute) Exposure:

No harmful effects were observed in rats exposed to 10 mg/m3 for 4 weeks.(4, unconfirmed)

Effects of Long-Term (Chronic) Exposure:

Bladder and kidney stones were observed in rats following ingestion of 3% isophthalic acid in the diet for 90 days.(2,unconfirmed)

Exposure of rats to 3% isophthalic acid in the diet for 90 days has led to the formation of bladder stones and kidney cancer.(2, unconfirmed) This carcinogenic effect is considered secondary to the development of bladder stones and does not reflect the direct carcinogenicity of isophthalic acid.(1)

Teratogenicity, Embryotoxicity and/or Fetotoxicity:
No significant toxic or teratogenic effects were observed in the mothers of offspring when pregnant rats were exposed to 9.07 mg/m3.(4,unconfirmed)


Selected Bibliography:
(1) Heck, H.d'A., et al. The induction of bladder stones by terephthalic acid, dimethyl terephthalate and melamin (2,4,6-triamino-s-triazine) and its relevance to risk assessment. Regulatory Toxicology and Pharmacology. Vol. 5, no. 3 (September, 1985). p. 294-313
(2) Park, C-H, et al. Phthalic acids and other benzenepolycarboxylic acids. In: Kirk-Othmer encyclopedia of chemical technology. 4th edition. Volume 18. John Wiley and Sons, 1996. p. 991--1043
(3) RTECS record for isophthalic acid. Last updated: 97O1
(4) MSDS database record for PIA (Amoco Chemical Company). Date of MSDS: 1997- 02-27
(5) HSDB record for isophthalic acid. Last revision date: 96/10/15
(6) The Sigma-Aldrich library of chemical safety data. Edition II. Volume 1. Sigma-Aldrich Corporation, 1988. p. 2028A
(7) Field, P. Dust explosions. Elsevier Scientific Publishing Company, 1982. p. 218
(8) Grossel, S.S. Safety considerations in conveying of bulk solids and powders. Journal of Loss Prevention in the Process Industries. Vol. 1 (April, 1988). p. 62-74
(9) Schwab, R.F. Dusts. In: Fire protection handbook. Edited by A.E Cote. 18th edition. National Fire Protection Association, 1997. p. 4-174 to 4-181
(10) Dean, J.A. Lange's handbook of chemistry. 14th edition. McGraw-Hill, Inc., 1992. p. 1.100
(11) Sheehan, R.J. Terephthalic acid, dimethyl phthalate and isophthalic acid. In: Ullmann's encyclopedia of industrial chemistry. 5th completely revised edition. Vol. A 26. VCH Verlagsgesellschaft, 1995. p. 193-204
(12) Leo, A., et al. Partition coefficients and their uses. Chemical Reviews. Vol. 17, no. 6 (December, 1971). p. 581
(13) Emergency action guide for terephthalic acid. Association of American Railroads, September, 1992
(14) Corrosion data survey: metals section. 6th edition. National Association of Corrosion Engineers, 1985. p. 96-16 to 97-16
(15) Elder, G.B. Materials of construction for organic acids. In: Process industries corrosion: the theory and practice. Edited by B.J. Moniz, et al. National Association of Corrosion Engineers, 1986. p. 287-296
(16) Forsberg, K., et al. Quick selection guide to chemical protective clothing. 3rd edition. Van Nostrand Reinhold, 1997.
(17) Workplace environmental exposure level guide. American Industrial Hygiene Association Journal. Vol. 56, no. 2, 1995. p. 202
(18) European Commission. Isophthalic acid. IUCLID Dataset. European Chemicals Bureau, Feb. 2000. Available at: <>

Information on chemicals reviewed in the CHEMINFO database is drawn from a number of publicly available sources. A list of general references used to compile CHEMINFO records is available in the database Help.

Review/Preparation Date: 1997-12-24

Revision Indicators:
Resistance of materials 1998-02-01
Bibliography 2006-03-03
Conversion factor 2006-10-05
Vapour density 2006-10-05
LFL/LEL 2006-10-05
UFL/UEL 2006-10-05

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